The key characteristics of cardiotoxicity for the pervasive pollutant phenanthrene.

The key characteristic (KCs) framework has been used previously to assess the carcinogenicity and cardiotoxicity of various chemical and pharmacological agents. Here, the 12 KCs of cardiotoxicity are used to evaluate the previously reported cardiotoxicity of phenanthrene (Phe), a tricyclic polycyclic aromatic hydrocarbon (PAH), and major component of fossil fuel-derived air pollution. Phe is a semi-volatile pollutant existing in both the gas phase and particle phase through adsorption onto or into particulate matter (PM). Phe can translocate across the airways and gastrointestinal tract into the systemic circulation, enabling body-wide effects. Our evaluation based on a comprehensive literature review, indicates Phe exhibits 11 of the 12 KCs for cardiotoxicity. These include adverse effects on cardiac electromechanical performance, the vasculature and endothelium, immunomodulation and oxidative stress, and neuronal and endocrine control. Environmental agents that have similarly damaging effects on the cardiovascular system are heavily regulated and monitored, yet globally there is no air quality regulation specific for PAHs like Phe. Environmental monitoring of Phe is not the international standard with benzo[a]pyrene being frequently used as a proxy despite the two PAH species exhibiting significant differences in sources, concentration variations and toxic effects. The evidence summarised in this evaluation highlights the need to move away from proxied PAH measurements and develop a monitoring network capable of measuring Phe concentration. It also stresses the need to raise awareness amongst the medical community of the potential cardiovascular impact of PAH exposure. This will allow the production of mitigation strategies and possibly the development of new policies for the protection of the societal groups most vulnerable to cardiovascular disease.

Polyaromatic hydrocarbons in pollution: a heart-breaking matter.

Air pollution is associated with detrimental effects on human health, including decreased cardiovascular function. However, the causative mechanisms behind these effects have yet to be fully elucidated. Here we review the current epidemiological, clinical and experimental evidence linking pollution with cardiovascular dysfunction. Our focus is on particulate matter (PM) and the associated low molecular weight polycyclic aromatic hydrocarbons (PAHs) as key mediators of cardiotoxicity. We begin by reviewing the growing epidemiological evidence linking air pollution to cardiovascular dysfunction in humans. We next address the pollution-based cardiotoxic mechanisms first identified in fish following the release of large quantities of PAHs into the marine environment from point oil spills (e.g. Deepwater Horizon). We finish by discussing the current state of mechanistic knowledge linking PM and PAH exposure to mammalian cardiovascular patho-physiologies such as atherosclerosis, cardiac hypertrophy, arrhythmias, contractile dysfunction and the underlying alterations in gene regulation. Our aim is to show conservation of toxicant pathways and cellular targets across vertebrate hearts to allow a broad framework of the global problem of cardiotoxic pollution to be established. AhR; Aryl hydrocarbon receptor. Dark lines indicate topics discussed in this review. Grey lines indicate topics reviewed elsewhere.

Kinematics and energetics of swimming performance during acute warming in brown trout Salmo trutta.

This study examined how acute warming of water temperature affects the mechanical efficiency of swimming and aerobic capabilities of the brown trout Salmo trutta. Swimming efficiency was assessed using the relationship between swimming kinematics and forward speed (U), which is thought to converge upon an optimum range of a dimensionless parameter, the Strouhal number (St ). Swim-tunnel intermittent stopped-flow respirometry was used to record kinematics and measure oxygen consumption (MO2) of S. trutta during warming and swimming challenges. Salmo trutta maintained St between 0·2 and 0·3 at any given U over a range of temperatures, irrespective of body size. The maintenance of St within the range for maximum efficiency for oscillatory propulsion was achieved through an increase in tail-beat frequency (ftail) and a decrease in tail-beat amplitude (A) as temperature increased. Maintenance of efficient steady-state swimming was fuelled by aerobic metabolism, which increased as temperature increased up to 18° C but declined above this temperature, decreasing the apparent metabolic scope. As St was maintained over the full range of temperatures whilst metabolic scope was not, the results may suggest energetic trade-offs at any given U at temperatures above thermal optima.

Cardiac function in an endothermic fish: cellular mechanisms for overcoming acute thermal challenges during diving.

Understanding the physiology of vertebrate thermal tolerance is critical for predicting how animals respond to climate change. Pacific bluefin tuna experience a wide range of ambient sea temperatures and occupy the largest geographical niche of all tunas. Their capacity to endure thermal challenge is due in part to enhanced expression and activity of key proteins involved in cardiac excitation-contraction coupling, which improve cardiomyocyte function and whole animal performance during temperature change. To define the cellular mechanisms that enable bluefin tuna hearts to function during acute temperature change, we investigated the performance of freshly isolated ventricular myocytes using confocal microscopy and electrophysiology. We demonstrate that acute cooling and warming (between 8 and 28°C) modulates the excitability of the cardiomyocyte by altering the action potential (AP) duration and the amplitude and kinetics of the cellular Ca(2+) transient. We then explored the interactions between temperature, adrenergic stimulation and contraction frequency, and show that when these stressors are combined in a physiologically relevant way, they alter AP characteristics to stabilize excitation-contraction coupling across an acute 20°C temperature range. This allows the tuna heart to maintain consistent contraction and relaxation cycles during acute thermal challenges. We hypothesize that this cardiac capacity plays a key role in the bluefin tunas' niche expansion across a broad thermal and geographical range.

The impact of abdominal aortic aneurysm surgery on intensive care unit resources in an Irish tertiary centre.

BACKGROUND: The potential impact of surgical service reconfiguration on intensive care unit (ICU) resources needs to be assessed. AIMS: To determine the resources required to provide post-operative ICU care to patients undergoing open abdominal aortic aneurysm (AAA) repair or endovascular aneurysm repair (EVAR) at a specialist centre in the HSE South area METHODS: For 198 patients, we calculated: (1) ICU bed-days; (2) organ support required; and (3) monetary cost of ICU care. RESULTS: In total, 82.8% (101/122) of patients undergoing open AAA repair required post-operative ICU care (52 emergency and 49 elective). Emergency cases required more ICU bed-days (median 4.2 vs. 1.9, p<0.0005) and were more likely to require ventilation (odds ratio, OR 11.7, p<0.0001), inotropes (OR 3.1, p=0.01) or enteral nutrition (OR 23.3, p<0.0001). Mean cost per patient was €3,956 for elective cases and €16,419 for emergency cases. No patient required ICU admission after EVAR (n=76). CONCLUSIONS: Open AAA surgery places significant demands on ICU resources. The planned reconfiguration of surgical services in Ireland must provide for parallel investment in ICU facilities and expertise.

The effect of stimulation frequency on the transmural ventricular monophasic action potential in yellowfin tuna Thunnus albacares.

Monophasic action potentials (MAPs) were recorded from the spongy and compact layers of the yellowfin tuna Thunnus albacares ventricle as stimulation frequency was increased. MAP duration decreased with increase in stimulation frequency in both the spongy and compact myocardial layers, but no significant difference in MAP duration was observed between the layers.

Warm fish with cold hearts: thermal plasticity of excitation-contraction coupling in bluefin tuna.

Bluefin tuna have a unique physiology. Elevated metabolic rates coupled with heat exchangers enable bluefin tunas to conserve heat in their locomotory muscle, viscera, eyes and brain, yet their hearts operate at ambient water temperature. This arrangement of a warm fish with a cold heart is unique among vertebrates and can result in a reduction in cardiac function in the cold despite the elevated metabolic demands of endothermic tissues. In this study, we used laser scanning confocal microscopy and electron microscopy to investigate how acute and chronic temperature change affects tuna cardiac function. We examined the temporal and spatial properties of the intracellular Ca2+ transient (Δ[Ca2+]i) in Pacific bluefin tuna (Thunnus orientalis) ventricular myocytes at the acclimation temperatures of 14°C and 24°C and at a common test temperature of 19°C. Acute (less than 5 min) warming and cooling accelerated and slowed the kinetics of Δ[Ca2+]i, indicating that temperature change limits cardiac myocyte performance. Importantly, we show that thermal acclimation offered partial compensation for these direct effects of temperature. Prolonged cold exposure (more than four weeks) increased the amplitude and kinetics of Δ[Ca2+]i by increasing intracellular Ca2+ cycling through the sarcoplasmic reticulum (SR). These functional findings are supported by electron microscopy, which revealed a greater volume fraction of ventricular SR in cold-acclimated tuna myocytes. The results indicate that SR function is crucial to the performance of the bluefin tuna heart in the cold. We suggest that SR Ca2+ cycling is the malleable unit of cellular Ca2+ flux, offering a mechanism for thermal plasticity in fish hearts. These findings have implications beyond endothermic fish and may help to delineate the key steps required to protect vertebrate cardiac function in the cold.

Hypercapnic acidosis reduces contractile function in the ventricle of the armored catfish, Pterygoplichthys pardalis.

The armored catfish, Pterygoplichthys pardalis (formerly Liposarcus pardalis), is a freshwater, facultative air-breathing teleost that experiences seasonal hypercapnia in the water systems of South America. We studied the tolerance of the P. pardalis heart to hypercapnic acidosis using an isolated ventricular muscle strip preparation. Force generation and kinetic variables were examined across a range of contraction frequencies under normocapnic and hypercapnic conditions in the absence and presence of sarcoplasmic reticulum (SR) inhibitors. Pterygoplichthys pardalis ventricle exhibited robust contractile force, on par with athletic fish species such as trout and tuna and a relatively flat force-frequency relationship between 0.2 and 1.5 Hz under normocapnic conditions (1% CO2, pH 7.78 +/- 0.02). Hypercapnic acidosis (7.5% CO2, pH 7.78 +/- 0.03) did not alter the shape of the force-frequency response but reduced force by approximately 50% across all frequencies tested, with only partial recovery upon return to normocapnic conditions. A subsequent and more severe acidotic challenge (15% CO2, pH 6.77 +/- 0.05) caused an additional 20% decrease in force. Force recovered to the level at which it had stablized after the first hypercapnic insult. SR inhibition had no steady state effect on force production at 0.2 Hz but resulted in a negative force-frequency relationship, suggesting that SR Ca2+ is recruited to a greater extent at high contraction frequencies. Surprisingly, SR-inhibited muscle was more resistant to hypercapnic acidosis (force decreased by approximately 40% across all frequencies) and displayed improved recovery upon return to normocapnic conditions. The significance of this latter finding is not clear. In aggregate, our results demonstrate robust contractile force, which extends across a range of frequencies and appears to be supported by SR Ca2+ cycling. Hypercapnic acidosis reduced contractile force but may provide preconditioning-like protection from subsequent insults.

Electrophysiological properties of the L-type Ca(2+) current in cardiomyocytes from bluefin tuna and Pacific mackerel.

Tunas are capable of exceptionally high maximum metabolic rates; such capability requires rapid delivery of oxygen and metabolic substrate to the tissues. This requirement is met, in part, by exceptionally high maximum cardiac outputs, opening the possibility that myocardial Ca(2+) delivery is enhanced in myocytes from tuna compared with those from other fish. In this study, we investigated the electrophysiological properties of the cardiac L-type Ca(2+) channel current (I(Ca)) to test the hypothesis that Ca(2+) influx would be large and have faster kinetics in cardiomyocytes from Pacific bluefin tuna (Thunnus orientalis) than in those from its sister taxon, the Pacific mackerel (Scombe japonicus). In accordance with this hypothesis, I(Ca) in atrial myocytes from bluefin tuna had significantly greater peak current amplitudes and faster fast inactivation kinetics (-4.4 +/- 0.2 pA/pF and 25.9 +/- 1.6 ms, respectively) than those from mackerel (-2.7 +/- 0.5 pA/pF and 32.3 +/- 3.8 ms, respectively). Steady-state activation, inactivation, and recovery from inactivation were also faster in atrial myocytes from tuna than from mackerel. In ventricular myocytes, current amplitude and activation and inactivation rates were similar in both species but elevated compared with those of other teleosts. These results indicate enhanced I(Ca) in atrial myocytes from bluefin tuna compared with Pacific mackerel; this enhanced I(Ca) may be associated with elevated cardiac performance, because I(Ca) delivers the majority of Ca(2+) involved in excitation-contraction coupling in most fish hearts. Similarly, I(Ca) is enhanced in the ventricle of both species compared with other teleosts and may play a role in the robust cardiac performance of fishes of the family Scombridae.

Acute temperature change modulates the response of ICa to adrenergic stimulation in fish cardiomyocytes.

The purpose of this study was to investigate how the endogenous catecholamine adrenaline protects sarcolemmal Ca(2+) flux through the L-type Ca(2+) channel (I(Ca)) during acute exposure to cold in the fish heart. We examined the response of I(Ca) to adrenergic stimulation at three temperatures (7 degrees, 14 degrees, and 21 degrees C) in atrial myocytes isolated from rainbow trout acclimated to 14 degrees C. We found that I(Ca) amplitude varied directly with test temperature and was increased by adrenergic stimulation (AD; 5 nM and 1 microM) at all temperatures. However, I(Ca) was significantly more sensitive to adrenergic stimulation at the coldest test temperature. In fact, at 7 degrees C in the absence of AD, I(Ca) was extremely low. The addition of 1 microM AD increased peak I(Ca) 7.2-fold at 7 degrees C, 2.6-fold at 14 degrees C, and 1.6-fold at 21 degrees C and ameliorated the temperature-dependent difference in Ca(2+) influx across the cell membrane. We suggest that this increased adrenergic sensitivity is a critical compensatory mechanism that allows the rainbow trout heart to maintain contractility during acute exposure to cold temperatures. In particular, the tonic level of adrenergic stimulation provided by circulating plasma catecholamines (i.e., in the nM concentration range) may be crucial for effective excitation-contraction coupling in the cold cardiomyocyte.

A comparison of myocardial beta-adrenoreceptor density and ligand binding affinity among selected teleost fishes.

This study quantified the cell surface beta-adrenoreceptor density and ligand binding affinity in the ventricular tissue of seven teleost species; skipjack tuna (Katsowonus pelamis), yellowfin tuna (Thunnus albacares), Pacific mackerel (Scomber japonicus), mahimahi (dolphin fish; Coryphaena hippurus), sockeye salmon (Oncorhynchus nerka), rainbow trout (Oncorhynchus mykiss) and an Antarctic nototheniid (Trematomus bernacchii). Beta-Adrenoreceptor density varied by almost fourfold among these species, being highest for the athletic fish: sockeye salmon among the salmonids and skipjack tuna among the scombrids. Beta-Adrenoreceptor density was lowest for the Antarctic icefish. Beta-Adrenoreceptor binding affinity varied by almost threefold. We conclude that there is a significant species-specific variability in myocardial beta-adrenoreceptor density and binding affinity and these interspecific differences cannot be attributed to temperature even though intraspecifically cold temperature can stimulate an increase in myocardial beta-adrenoreceptor density. Instead, we suggest that interspecifically myocardial beta-adrenoreceptor density is highest in fish that inhabit tropical water.

Temperature-dependence of L-type Ca(2+) channel current in atrial myocytes from rainbow trout.

Rainbow trout, Oncorhynchus mykiss, inhabit eurythermal environments and must therefore be able to cope with changes in environmental temperature. As ectotherms, their heart is required to maintain cardiac function over a range of ambient water temperatures. This raises important questions concerning the temperature-dependence of cardiac ion channel function in fish hearts, in particular, the channels involved in Ca(2+) transport. Thus, we studied the effects of acute, physiologically relevant temperature changes on the density and kinetics of the L-type Ca(2+) channel current (I(Ca)) in rainbow trout atrial myocytes using the whole-cell patch-clamp technique. Myocytes from fish acclimated to 14 degrees C were first tested at 14 degrees C, then at 21 degrees C and finally at 7 degrees C. Using a square-pulse voltage-clamp in the first series of experiments, the peak density of I(Ca) increased (Q(10)=1.9) as temperature was increased from 14 to 21 degrees C and decreased (Q(10)=2.1) as temperature was decreased from 14 to 7 degrees C. In contrast to current density, the charge carried by I(Ca) was inversely related to temperature as a result of changes in the kinetic properties of the channel; both the fast (tau(f)) and slow (tau(s)) components of inactivation were slower at 7 degrees C than at 14 and 21 degrees C. Action potentials were recorded at the three test temperatures and then used as voltage-clamp stimulus waveforms to reassess I(Ca) in a second series of experiments. While the temperature-dependency of I(Ca) was similar to that found with the square-pulse voltage-clamp, the charge carried by I(Ca) was temperature-independent. These results show that the temperature-dependency of I(Ca) in rainbow trout is in the lower range of that reported in mammals and, although this could have profound effects on Ca(2+) delivery to the myofilaments, the temperature-induced modifications in the action potential may help to maintain a fairly constant Ca(2+) delivery during an acute temperature change in rainbow trout.

TRAF4 deficiency leads to tracheal malformation with resulting alterations in air flow to the lungs.

TRAF4 is one of six identified members of the family of TNFR-associated factors. While the other family members have been found to play important roles in the development and maintenance of a normal immune system, the importance of TRAF4 has remained unclear. To address this issue, we have generated TRAF4-deficient mice. Despite widespread expression of TRAF4 in the developing embryo, as well as in the adult, lack of TRAF4 expression results in a localized, developmental defect of the upper respiratory tract. TRAF4-deficient mice are born with a constricted upper trachea at the site of the tracheal junction with the larynx. This narrowing of the proximal end of the trachea results in respiratory air flow abnormalities and increases rates of pulmonary inflammation. These data demonstrate that TRAF4 is required to regulate the anastomosis of the upper and lower respiratory systems during development.

The effect of ryanodine on isometric tension development in isolated ventricular trabeculae from Pacific mackerel (Scomber japonicus).

An isometric muscle preparation was used to study the inhibitory effect of ryanodine on contractile function in isolated ventricular trabeculae of the Pacific mackerel (Scomber japonicus). Ryanodine (an inhibitor of sarcoplasmic reticulum (SR) function) caused a 20% reduction in peak tension at 20 degrees C, but not 15 degrees C, over the range of frequencies (0.2-3.0 Hz) tested. This indicates that in the absence of a functional SR, the mackerel ventricle can maintain most of its contractile strength utilizing other modes of Ca(2+) delivery to the myofilaments. Ca(2+) flux through the sarcolemmal (SL) L-type Ca(2+)-channels is most likely the predominant pathway for Ca(2+) activation of the myofilaments, although reverse mode Na(+)/Ca(2+) exchange could potentially contribute to a significant extent. High levels of adrenergic stimulation overwhelmed the negative inotropy caused by ryanodine, returning tension to pre-ryanodine levels, further suggesting that the mackerel ventricle can maintain contractile function without Ca(2+) contribution from the SR. These results are discussed within the context of what is known about SR Ca(2+) utilization in rainbow trout and tuna hearts.

The combined functions of proapoptotic Bcl-2 family members bak and bax are essential for normal development of multiple tissues.

Proapoptotic Bcl-2 family members have been proposed to play a central role in regulating apoptosis. However, mice lacking bax display limited phenotypic abnormalities. As presented here, bak(-/-) mice were found to be developmentally normal and reproductively fit and failed to develop any age-related disorders. However, when Bak-deficient mice were mated to Bax-deficient mice to create mice lacking both genes, the majority of bax(-/-)bak(-/-) animals died perinatally with fewer than 10% surviving into adulthood. bax(-/-)bak(-/-) mice displayed multiple developmental defects, including persistence of interdigital webs, an imperforate vaginal canal, and accumulation of excess cells within both the central nervous and hematopoietic systems. Thus, Bax and Bak have overlapping roles in the regulation of apoptosis during mammalian development and tissue homeostasis.

Expression and function of CTLA-4 in Th1 and Th2 cells.

CTLA-4 is expressed on T cells after activation and shares homology with the CD28 costimulatory receptor. In contrast to CD28, CTLA-4 is thought to be a negative regulator of T cell activation. Cross-linking of CTLA-4 during activation of peripheral T cells reduces IL-2 production and arrests T cells in G1. Much less is known about the function of CTLA-4 in differentiated T cells. We have investigated the expression and function of CTLA-4 in established Th1 and Th2 clones and in bulk populations of Th1 and Th2 cells freshly derived in vitro from TCR transgenic splenocytes. We found that CTLA-4 was induced under similar conditions and with similar kinetics following activation of both Th1 and Th2 clones. However, CTLA-4 expression was much higher in Th2 than Th1 clones and lines. This was confirmed by flow cytometry, confocal microscopy, and Northern blot analysis. The ratio of surface to intracellular expression of CTLA-4 and its rate of endocytosis were similar in Th1 and Th2 clones. Inhibition of binding of CTLA-4 to its ligands using soluble anti-CTLA-4 mAb during stimulation with Ag increased the production not only of IL-2 by Th1 clones, but also that of IL-3 and IFN-gamma by Th1 clones and of IL-3, IL-4, IL-5, and IL-10 by Th2 clones. In contrast, when anti-CTLA-4 was coimmobilized with anti-CD3 and anti-CD28 mAbs, a decrease in the production of multiple cytokines was observed. We conclude that CTLA-4 can function to suppress the production of cytokines produced by both Th1 and Th2 cells.

The effect of temperature and adrenaline on the relative importance of the sarcoplasmic reticulum in contributing Ca2+ to force development in isolated ventricular trabeculae from rainbow trout

The sarcoplasmic reticulum (SR) is central to intracellular Ca2+ regulation during excitation­contraction (E-C) coupling in mammalian cardiac tissue. The importance of the SR to E-C coupling in lower vertebrates is less certain. This uncertainty can be attributed, in part, to the temperature-dependency of the SR Ca2+-release channel and to interspecific differences in the ryanodine-sensitivity of ectotherm cardiac muscle. Furthermore, the relative importance of the SR in contributing intracellular Ca2+ to force development may be influenced by adrenergic stimulation, which increases trans-sarcolemmal (extracellular) Ca2+ influx. The objective of this study was to assess the relative importance of SR (intracellular) and sarcolemmal (SL; extracellular) Ca2+ fluxes during the isometric contraction of isolated ventricular trabeculae from rainbow trout Oncorhynchus mykiss. To approximate in vivo Ca2+ availability to the muscle better, a tonic level (10 nmol l-1) of adrenaline was used in all control experiments, and SL Ca2+ influx was stimulated with high levels (10 µmol l-1) of adrenaline. Ryanodine, a noted blocker of SR Ca2+ release in mammals, was used to assess SR involvement. To examine the role of temperature on the relative Ca2+ contribution from each source, experiments were performed at two temperatures (12 and 22 °C), using ventricular trabeculae from fish acclimated to both 12 and 22 °C. Under all test conditions studied, SL Ca2+ influx was the primary source of activator Ca2+, as assessed by the change in isometric force after ryanodine application. Even so, the SR contribution of activator Ca2+ was significantly greater at a test temperature of 22 °C than at 12 °C. We attribute this observation to the temperature-dependent nature of the SR Ca2+-release channel. At 22 °C and under control conditions, ryanodine reduced peak tension at all pacing frequencies (by approximately 50 % at 0.2 Hz, approximately 25 % at 1.2 Hz and approximately 20 % at 2.0 Hz), regardless of acclimation temperature. Therefore, the SR is a significant, but secondary, contributor of activator Ca2+ for tension development at warm temperatures. The magnitude of SR Ca2+ contribution was inversely related to pacing frequency, but remained significant at physiological pacing frequencies. This was a novel finding. The degree of ryanodine-sensitivity in the present study was greater than that reported previously for the rainbow trout. We attribute this difference to the use of tonic adrenergic stimulation in the present study. In contrast to the experiments at the warmer test temperature, at 12 °C and under control conditions, ryanodine significantly reduced peak tension only at low frequencies (by approximately 25 % at 0.2 Hz), regardless of acclimation temperature. These findings suggest that at cold temperatures, and at physiologically relevant pacing frequencies, the SR may not be important in supplying Ca2+ to the contractile elements of the trout heart. At both test temperatures and regardless of acclimation temperature, stimulation with 10 µmol l-1 adrenaline caused positive inotropy of sufficient magnitude to ameliorate the negative inotropic effect of ryanodine completely, with the exception of high pacing frequencies (>1.2 Hz) at 22 °C, where adrenergic stimulation did not fully compensate for the effects of ryanodine. This exception is discussed in relation to the reduced adrenergic sensitivity of the trout myocardium at warm temperatures. The adrenergically mediated compensation for the loss of the SR Ca2+ supply is a novel finding for fish hearts. Therefore, while our study clearly demonstrates that the relative importance of SR Ca2+ release is subject to temperature and frequency, adrenaline-mediated increases in SL Ca2+ influx decrease the importance of the SR in contributing Ca2+ to E-C coupling in trout ventricular myofilaments.

A conserved family of cellular genes related to the baculovirus iap gene and encoding apoptosis inhibitors.

The baculovirus inhibitor of apoptosis gene, iap, can impede cell death in insect cells. Here we show that iap can also prevent cell death in mammalian cells. The ability of iap to regulate programmed cell death in widely divergent species raised the possibility that cellular homologs of iap might exist. Consistent with this hypothesis, we have isolated Drosophila and human genes which encode IAP-like proteins (dILP and hILP). Like IAP, both dILP and hILP contain amino-terminal baculovirus IAP repeats (BIRs) and carboxy-terminal RING finger domains. Human ilp encodes a widely expressed cytoplasmic protein that can suppress apoptosis in transfected cells. An analysis of the expressed sequence tag database suggests that hilp is one of several human genes related to iap. Together these data suggest that iap and related cellular genes play an evolutionarily conserved role in the regulation of apoptosis.

Maximum cardiac performance of rainbow trout (Oncorhynchus mykiss) at temperatures approaching their upper lethal limit

Numerous studies have examined the effect of temperature on in vivo and in situ cardiovascular function in trout. However, little information exists on cardiac function at temperatures near the trout's upper lethal limit. This study measured routine and maximum in situ cardiac performance in rainbow trout (Oncorhynchus mykiss) following acclimation to 15, 18 and 22 °C, under conditions of tonic (30 nmol l-1), intermediate (60 nmol l-1) and maximal (200 nmol l-1) adrenergic stimulation. Heart rate increased significantly with both temperature and adrenaline concentration. The Q10 values for heart rate ranged from 1.28 at 30 nmol l-1 adrenaline to 1.36 at 200 nmol l-1 adrenaline. In contrast to heart rate, maximum stroke volume declined by approximately 20 % (from 1.0 to 0.8 ml kg-1) as temperature increased from 15 to 22 °C. This decrease was not alleviated by maximally stimulating the heart with 200 nmol l-1 adrenaline. Because of the equal and opposite effects of increasing temperature on heart rate and stroke volume, maximum cardiac output did not increase between 15 and 22 °C. Maximum power output decreased (by approximately 10-15 %) at all adrenaline concentrations as temperature increased. This reduction reflected a poorer pressure-generating ability at temperatures above 15 °C. These results, in combination with earlier work, suggest (1) that peak cardiac performance occurs around the trout's preferred temperature and well below its upper lethal limit; (2) that the diminished cardiac function concomitant with acclimation to high temperatures was associated with inotropic failure; (3) that Q10 values for cardiac rate functions, other than heart rate per se, have a limited predictive value at temperatures above the trout's preferred temperature; and (4) that heart rate is a poor indicator of cardiac function at temperatures above 15 °C.

Genomic organization of mouse and human Bruton's agammaglobulinemia tyrosine kinase (Btk) loci.

Btk is a cytoplasmic protein tyrosine kinase (PTK) that has been directly implicated in the pathogenesis of X-linked agammaglobulinaemia (XLA) in humans and X-linked immunodeficiency (Xid) in mice. We have isolated phage and cosmid clones that allowed us to deduce the genomic structure of mouse and human Btk loci. The mouse and human genes are contained within genomic regions that span approximately 43.5 kb and 37.5 kb, respectively. Both loci contain 18 coding exons ranging between 55 and 560 bp in size with introns ranging in size from 164 bp to approximately 9 kb. The 5'-untranslated regions are encoded by single exons located approximately 9 kb upstream of the first coding exon. Exon 18 encodes for the last 23 carboxyl-terminal amino acids and the entire 3'-untranslated region. The location of intron/exon boundaries in the catalytic domains of the mouse and human Btk loci differs from that found in other described sub-families of intracellular PTKs, namely that of Src, Fes/Fer, Csk, and Abl/Arg. This observation is consistent with the classification of Btk together with the recently characterized kinases, Tec and Itk, into a separate sub-family of cytoplasmic PTKs. Putative transcription initiation sites in the mouse and human Btk loci have been determined by using the rapid amplification of cDNA ends assay. Similar to many other PTK specific genes, the putative Btk promoters lack obvious TATAA and CAAAT motifs. Putative initiator elements and potential binding sites for Ets (PEA-3), zeste, and PuF transcription factors are located within the 300 bp which are located upstream of the major transcription start site in both species. These sequences can mediate promoter activity when placed upstream of a promotorless chloramphenicol acetyl transferase reporter gene in an orientation-dependent manner. The present analysis will significantly facilitate the mutational analyses of patients with XLA and the further characterization of the function and regulation of the Btk molecule.